A mining farm, as the name suggests is when multiple miners come together for advantageous reasons such as saving on energy costs. Mining firms can be as trivial as a room solely dedicated to mining, or a large warehouse featuring multiple GPUs and mining rigs.
Mining farms are often managed by multiple people. Essentially a mining farm is a mining pool where the miners are based within a single location. Mining hardware also consumes more energy, while dissipating substantial heat.
That is why mining farms are often set up in locations with low temperatures to prevent overheating without the use of air conditioners. Some other ideal locations include places with the lowered electricity cost as well.