Relevance of the word 'ICTHUS' I would like to know the meaning and the importance of the word 'ICTHUS' among Christians. I have learned that this is some sort of symbol. Can anyone help me on this?
ΙΧΘΥΣ means fish in an old form of Greek. It now primarily refers to a particular Christian fish symbol. From Wikipedia:


  Ichthys (also Ichthus or Ikhthus /ˈɪkθəs/), from the Koine Greek word for fish: ἰχθύς, (capitalized ΙΧΘΥΣ or ΙΧΘΥϹ) is a symbol consisting of two intersecting arcs, the ends of the right side extending beyond the meeting point so as to resemble the profile of a fish, used by early Christians as a secret Christian symbol and now known colloquially as the "sign of the fish" or the "Jesus fish."


The word itself has symbolic meaning, though. Saint Augustine gives the following symbolic explanation in City of God:


  But if you join the initial letters of these five Greek words, ᾽Ιησοῦς Χριστος Θεοῦ υἰὸς σωτήρ, which mean, “Jesus Christ the Son of God, the Saviour,” they will make the word ἰχδὺς, that is, “fish,” in which word Christ is mystically understood, because He was able to live, that is, to exist, without sin in the abyss of this mortality as in the depth of waters.


For the symbolic meaning of fishes and the "fish symbol", you could ask:


Why are fish in general a Christian symbol?
What is the historical significance/origin of the fish symbol called "ΙΧΘΥΣ"?
Why is the fish often used as a symbol of Christ?