Since everyone else here has focused their attention on laws in India, and included some very insulting and offensive definitions, let me answer your question from the perspective of someone that's actually done it!
Primarily, let me first confirm that I’ve carried 5 babies as a surrogate and I’ve never been to India, so surrogacy does actually happen in other places besides India. I’ve carried for European Caucasians, Canadian Jews, a Canadian man of European stock and Canadian-born Caucasians, in that order. Not one was Indian, so other people besides Indians do access surrogacy.
But you asked for a definition, and IR