Someone who's always nice, helpful and a basic moral support for just about anyone. Suppresses his (or her) own needs in order to please or satisfy (the needs of) others. The people's pleaser won't bother you with his or her own needs and problems, as this person is too keen on helping out others.
Great danger of being used (in the negative way)!!
In fact this is what girls should look for in a guy when looking for proper/stable "relationship material" (I guess), however, in some way this hardly ever results in a woman being either physically or sexually attracted. A people's pleaser is more likely to be put in the friends zone straight away, without even being considered dating material. Obviously this also works the other way around, where the girl is in the pleaser's role. But, as a fact, guys won't put the "pleaser" girls in a confined area called the friends zone as easily as girls would.
Closely related to being a nice guy, and unfortunately is as probable to lead to one-sided relationships. Where all the empathy and consideration comes merely from the people's pleaser, and for the good of the other person.
"Harry is suchs a nice guy, he's just a people's pleaser."
"Thanks for helping me out again, Mary, as always, you are too kind!"
After dating a girl for a while, she might tell you that:
"You're too good for me, you're such a people's pleaser. I see you as a friend/brother, rather than someone I'm physically or sexually attracted to."