Hlo Friends,
Can anyone tell me, What is a long-tail keyword, and what is an LSI keyword?

Long tail keywords are simply an expression of the number of terms in a keyword. Anything over 4 phrases are termed long tail keywords.

LSI is more to do with the relevance of the keyword to the original keyword. If you are focusing on the keywords "mobile online", "mobile price", "cell phone mobile rating" "mobile technology characteristics" may be related to Original keyword.

Long tail keywords are those three and four keyword phrases which are very, very specific to whatever you are selling.