What is Imaan?

From: http://quranicteachings.co.uk/imaan.htm

The root of the word IMAAN is A-M-N, which primarily means "to trust, be secure, be in safety, confine in". The word IMAAN has the following meanings:
-The believing or Belief or Conviction
-Becoming true to the trust with respect to which Allah Has confided in one, by a firm believing with the heart, not by profession of belief with the tongue only, without the assent of the heart
-The manifesting humility or submission, and the accepting of the Divine Law and the firm believing thereof with the heart
-Faith
-Trust
-Confidence
-Acknowledgement
-Submission

What is IMAAN about?
IMAAN is about having a firm believing with the heart in 5 Realities [2:177]:
1. Allah
2. The Hereafter
3. Malaika (angels)
4. The Divine Guidance
5. The Prophets
The one who believes in the above five realities is Momin and the one who denies or rejects them is not Momin [4:136].

The most important point is that IMAAN in the above should be with the concept of these that is given in Quran. IMAAN on the manmade concept of Allah, the hereafter, Malaika, the Divine Guidance and the Prophets, is not the correct IMAAN.

Another reality that is mentioned in context of IMAAN is AL-GHAIB {Unseen} [2:3]. There are different types of UNSEEN described in Quran. The following are some examples:
Allah is UNSEEN [21:49, 35:18, 36:11, 50:33, 67:12]
Life after death is UNSEEN [27:65-66]
Everlasting paradise in the hereafter is UNSEEN[19:61] AL-SAA'AT [the day of judgment] is UNSEEN [16:77, 32:5-6, 34:3, 72:25-26]
The WAHI [revelation], before it is revealed, is UNSEEN [3:44, 11:49, 81:24]
Something/Someone that is not in front of our eyes [i.e. absent] is UNSEEN [12:52] The events of the past , of which we do not have knowledge, may be UNSEEN [18:25-26]

IMAAN in the Unseen is the IMAAN in Allah, the Hereafter and the Unseen consequences of our actions which has not yet manifested
There is no mention of IMAAN on TAQDEER or pre-destination in the Quran.

The importance of Reason in IMAAN
And do not follow (blindly) any information of which you have no (direct) knowledge. (Using your faculties of perception and conception, you must verify it for yourself. (In the Court of your Lord,) you will be held accountable for your hearing, sight, and the faculty of reasoning." [17:36]

The Believers (Mu'minin) according to the Qur'an, are:
[25:73] "Those who, when the revelations of their Rabb (Nourisher and Sustainer) are presented to them, do not fall thereat deaf and blind."
[8:22] "The worst of beasts in the sight of Allah are the deaf and dumb who do not use their intellect to understand."
[7:179] "There are many among Jinns and human beings, who lead such a life as makes it obvious that they are meant for Hell. They have hearts wherewith they understand not, they have eyes wherewith they see not, and they have ears wherewith they hear not; they are like cattle-nay, are worse; they are the heedless."

Just SAYING that "I am a believer" does not make one a believer
"And there are some people who say: We believe in Allah and the last day; and they are not at all believers." [2:8]
IMAAN is not just "uttering something with the tongue"; it is a strong conviction from the bottom of the heart [5:41, 49:14]
IMAAN is not "saying" something but "doing" something [2:8, 61:2-3]
There are real tests to see whether we are true believers or not [29:2-3]

True believers are those:
-Who bow down or submit themselves with obedience to Allah and follow His Commands [5:55, 32:15, 2:121]
-Who work deeds of righteousness [17:9, 18:2]
-Who strive with their wealth and lives in the cause of Allah [8:74, 49:15]
-Who give themselves and their wealth in the cause of Allah [9:111]
-Who establish As-Salat [8:2-4, 5:55]
-Who set up the system of ZAKAAT [5:55] and spend their wealth (for the welfare of humanity) [8:2-4]
Important
And do not follow (blindly) any information of which you have no (direct) knowledge. (Using your faculties of perception and conception, you must verify it for yourself. (In the Court of your Lord,) you will be held accountable for your hearing, sight, and the faculty of reasoning."[17:36]