It depends on what feed that betting site takes their football content from. Opta is very popular with the bookmakers and they define a shot on target as:
any shot that goes into the net regardless of whether it was meant as a shot or not - e.g. a cross that goes in.
any shot at goal that is saved by the goalkeeper which was definitely going in.
a block by a player if they are the last line of defence and the keeper has no chance of saving.
Shots can be classified as with your foot or head. It's worth noting that sometimes there is a grey area as to whether a shot on target has been counted so it's worth keeping an eye on social media, especially @BettingOddsUK if it's a featured football tip on our site as we'll be watching the game like a hawk looking for the win!