Surroundings
Everything outside the chosen system with which it can exchange energy or matter.
Unit
Dimensionless
In depth
In practice the surroundings are treated as the immediate environment — the solvent, the calorimeter and the laboratory air — since distant regions have no measurable effect. Because the surroundings are effectively infinite, absorbing heat from a reaction changes their temperature negligibly.
Examples in the real world
The water bath around a reaction vessel; the atmosphere absorbing heat from a burning candle.