To warm in cooking means to raise the temperature of something, though occasionally you will be instructed to let the temperature of something cool from hot down to warm.
What is considered “warm” depends on what you are talking about.
A warm oven is considered by some to be around 140 F (60 C); by others to be about 325 F (170 C / gas mark 3.)
When referring to the actual food, it’s presumed to be a temperature between 105 F to 115 F (40 to 46 C.)