Salaam alaikum (peace be upon you),
This is an interesting question, could I ask what prompted you to ask?
Am I correct when you say kaf you mean this letter? ك
From my, limited understanding, it is a letter of the Arabic alphabet and appears throughout the Qur'an such as in this word الْكِتَابُ meaning book
The letter also appears among the disjoined letters of the Qur'an which precede a number of surahs such as the following at the start of Surat Maryam
Kaf, Ha, Ya, 'Ayn, Sad correspondingly.
The meaning of these letters is for Allah alone, if you're interested
here's an informative article on the subject
Also a good lecture on the first instance of these disjoined letters
[youtube]gWJnc4J9x1s[/youtube]
The Meaning of Alif, Lam, Meem - Nouman Ali Khan - YouTube
As for anything else specifically related to Kaf I'm not a linguist nor well versed to explain such a topic though I am aware of a tradition attributed to another letter the ba as well as the nukta (dot)
On that note, Imam ‘Ali (AS) testifies: "Know that all the wisdom of the Heavenly Scriptures are in The Qur'an and whatever is in The Qur'an is in the Fatiha (Suratul Hamd) and whatever is in Fatiha is in Bismillah and whatever is in Bismillah is in the ‘Ba’ of Bismillah and whatever is in the ‘Ba’ of Bismillah is encapsulated in the dot under ‘Ba’; and I am that dot under ‘Ba’." (Yanabee’ Al Mawadda)
Which is part of a further understanding of the significance and vastness of such terms in the following post
http://www.religiousforums.com/forum/islam-dir/151318-exegis-basmala.html#post3419767
I hope others can add their knowledge here as well.