Apparently it relates to duplicate bridge. Initially, I thought it meant playing the hand in a risky way to score overtricks, and taking the chance of sacrificing a potential game. But then someone said that you could "play for top or bottom" by making a safety play that others don't make. The term he used was "going against the field." What did he mean by this?
This answer is specific to Matchpoints. In Matchpoints, playing for top or bottom means that if you succeed, you get a top, otherwise you get a bottom. (Note: I haven't heard of people talking about top/bottom in other forms of duplicate).
Any play could potentially be called this way, including safety plays.
To give a specific example of where a safety play might be considered playing for top or bottom, consider the following hand:
You are playing matchpoints and have reached the contract of 6♠. You also think that the rest of players in your direction will do the same. Say you get a club lead.
Now if this were rubber bridge, you could almost ensure 12 tricks by winning the club K and playing a low spade towards the 7. If RHO follows, you play the 7. If RHO shows out, you win the K and play toward the AT. LHO can only get one spade trick (barring really bad breaks in other suits).
Basically, ducking the first round of spades is a safety play to cater to QJxx spades with one of the opponents.
At Matchpoints, however, the normal play is to bang down the AK, making 13 tricks if trumps are 2-2 and still have chances for making 13 if they are 3-1 with a singleton Q or J.
Assuming the field will not take the safety play, by taking the safety play ("going against the field"), you get a top if QJxx is held by one opponent (and rest of the field goes down by guessing to cash the honour in the wrong hand first). You will get a bottom if trumps are 2-2, or there is a singleton Q or J (you make exactly 12 tricks, while the rest make 13).
We ignore QJx, as we expect opponents to split QJ and ensure a trick. You get an average in that case (everyone makes exactly 12 tricks).