1. Contract law.
A required element in a contract under English law by which something of value, including a promise, is exchanged for the act or promise of another.
Note that other legal systems may differ significantly.
For example in Scots law a unilateral undertaking that is intended to have legal effect, such as a promise, is legally binding (without the need for consideration to pass from the recipient of the promise).
2. ACT Ethical Code.
To act with courtesy and consideration is one of the principles of the ACT's Ethical Code.
3. Behavioural skills.
More generally, thoughtfulness and sensitivity towards others.