I this post I want to throw some light on the meaning of the word and
the importance of the word pertaining to the religion Islam.

First of all Jihaad is a noun in Arabic language. The root word is Jhud
which means "effort". If you know Urdu, there is a word which we
normally use, Jidd-o-Jahad. Meaning to work hard. Another related word
in Arabic is "ijtihad", meaning "working hard or diligently".

Jihaad is simply the process of "exerting the best efforts", involving
some form of "struggle" and "resistance", to achieve a particular goal.
In short Jihaad means struggle against, or resistance to, something for
the sake of a goal. This is the generic meaning of the word Jihaad,
which is independent of the applied efforts or the intended goal.

If you have a particular goal in mind and you are putting your utmost
effort to achieve the goal then you are doing Jihaad in that way.

I would like to put few verses of the Quran where the word Jihaad has
come.

[31:14] And We have enjoined on man (to be dutiful and good) to his
parents. His mother bore him in weakness and hardship upon weakness and
hardship, and his weaning is in two years - give thanks to Me and to
your parents. Unto Me is the final destination.
[31:15] But if they (both) [jahadaka] "strive with you" to make you join
in worship with Me others that of which you have no knowledge, then obey
them not; but behave with them in the world kindly, and follow the path
of him who turns to Me in repentance and in obedience. Then to Me will
be your return, and I shall tell you what you used to do.

[49:15] The (true) believers are those only who believe in Allah and His
messenger and afterward doubt not, but [jahadu] "strive with" their
wealth and their lives for the cause of Allah. Such are the sincere.

Active participle of the word Jihaad is Mujahid (masculine) and Mujahida
(feminine).

If you have any doubts you can always ask in the comments section.

The word Deen is another Arabic word which is roughly translated as
religion. To know what Deen is we actually should know what the word
religion means in English.

"Religion: a set of beliefs concerning the cause, nature, and purpose of
the universe, esp. when considered as the creation of a superhuman
agency or agencies, usually involving devotional and ritual observances,
and often containing a moral code governing the conduct of human
affairs." - dictionary.com

The most important point to consider here is that the word religion
usually is connected with the man's personal life, especially in the
area of worship. This gives us the notion that the God, in which a
person believes, guides him only in his personal life in the field of
worship.

If God is the Supreme the Almighty, the One Who has created the whole
universe and the Sustainer of it, then He must be guiding us in every
aspect of our life. Be it in the areas of business, politics, moral
conduct or how to protect our family, our society, our country etc. In
short the complete way of life.

So the word Deen is nothing but the "complete way of life". There is a verse in Quran which says: The Deen acceptable by the
Almighty is Islam. Which actually means: The (complete) way of life
acceptable by the Almighty is to submit your will to the Will of
Almighty God.

Islam is an Arabic word. It is derived from two root words, Salaam and
Slm. The word Salaam means Peace. As it is usually used while greeting
someone. And the word Slm means Submission or Obedience.

By combining these two words we get the word Islam. So the word Islam
means to get Peace by Submitting your will to the Almighty. In other
words it stands for complete submission or obedience to the One Who has
power over you. Simply to say, there is an unalterable law and you
follow it, which means you are following Islam.

For example the planets around the Sun. They are following a set of
laws, which means they are following Islam. Same way the Sun the moon
the stars and all the heavenly bodies are knit together in a splendid
system. They follow an unalterable law and do not make even a slightest
deviation from this course. Together they are peaceful with each other.
If they deviate from their ordained course they end up in destruction.
Their wont be peace. The one who (or the thing which) follows Islam in a complete way is
called a Muslim. For example the eye is a Muslim, as it is ordained to
see, it follows the law of seeing, it follows Islam. In fact every organ
in the body is governed by laws prescribed to them. If I use any of my
organs to do something which it is not supposed to do, then I end up
harming it.

Hence the word Islam has nothing to do with religion. It is an
independent word which means submission and obedience to the All
Powerful.

Why Muslims prefer to use the word Allah instead of the English word God or for that matter any other words used in any other language?

Allah is an Arabic word. It is derived from the word ilah or Elah. Which means "A thing (can be anything or anyone) or deity worthy of worship". In English it can be the word god. The plural of ilah is Aliyah. The feminine is ilahah.

In English there is a definite article called "The", in Arabic also there is a definite article called "Al". If you prefix a noun with Al it becomes definite. For example "Kitab" (Book) is a noun in Arabic. And if you prefix it with "Al" it becomes "Al-Kitab" which means "The book". It actually means a particular book.

Same way if you prefix Al to the word "ilah" of Arabic it becomes "Al-ilah". The letters of Arabic Alif, Laam, Hamza, Laam, Alif and Hai which make "Al-ilah". When the letter Hamza comes after the letter Laam the voice of Hamza is dropped. Resulting in "Al-lah". Then the two Laams geminate, making it sound "Allah".

So the word Allah in Arabic is nothing but, "The God". And the WORD Allah has no gender. There is no feminine word for Allah. There is no plural for the WORD Allah. As mentioned earlier, the word ilah is masculine and has feminine as well as plural word. But the word Allah is neither masculine nor feminine and has no plural. There can be neither prefix nor postfix to the word Allah. It is because of the grammar of Arabic.

Like if you add father to the word God, it becomes "God father". But you cannot add "Abi" (father) to the word Allah. It becomes meaningless even if you try to add, the whole grammar is lost.

Allah is a word used to refer God not just by Muslims. Even the Jews and Christian who speak Arabic use this word. Allah was the word used by people even before the Prophet Muhammad came.

So just in case you don’t know, Allah is not a Muslim God. The Muslims who refer Allah is not just the God of them. He is the God of everyone. He is the God of you and me. The One Who created the Heavens and the Earth.