The half volley is a tennis shot but why this word entered in cricket and what is half volley shot of cricket?
Actually, the Half-volley is not a shot type but a delivery type (in terms of pitching). This type of delivery pitches ahead of a good length but not too fuller(which ends up in full-toss). I.e. it pitches between good length and full toss. Batsmen can easily drive such delivery.
May be the reason behind it's name is: The ball pitches near foot same as in tennis.
See the terms in a glossary of cricket terms by ESPNCricinfo.