Could you explain what is meant by the term 'contract' in the context of software development?

In software development, a contract is an agreement between system components about how they should interact. It defines the obligations and guarantees of each party.

For example, a contract may describe:

• What input data a function or module accepts.
• What output data or effects are guaranteed.
• Preconditions (what must be true before the call).
• Postconditions (what will be true after execution).

This helps improve the reliability and predictability of the code, and facilitates testing and maintenance.

In Android, for instance, a contract can be an interface that defines the methods to be implemented and the expected behavior of these methods.