Something lukewarm is just a teeny bit warm. Lukewarm feelings are also not very strong.
Lukewarm is a word for things that are warm, but only barely. A forgotten cup of hot coffee will get lukewarm before it eventually gets cold. It's disappointing when food at a restaurant is served lukewarm; most people like their food hot. Also, people can have lukewarm feelings and reactions. If someone asks you out to lunch and you say, "Well, I guess that would be OK," that's a lukewarm response.