What is the difference between a contract and an interface in Solidity?

In Solidity, a contract is a unit of code that can contain data and functions that can be invoked and interacted with. A contract can be used to represent a real-world entity, such as a token, an agreement, or a voting system.

While An interface is a way of specifying the functions that a contract must implement, without providing an implementation for those functions. Interfaces are used to define a common set of functions that multiple contracts can implement, allowing them to be used interchangeably.

Here are some key differences between contracts and interfaces in Solidity:

• Implementation: Contracts contain both a definition and an implementation for the functions they define, while interfaces only contain a definition.
• Inheritance: Contracts can inherit from other contracts, while interfaces cannot be inherited from.
• State: Contracts can have their own state, while interfaces do not have state.
• Instances: A contract can have multiple instances, each with its own unique state. Interfaces cannot be instantiated and do not have their own state.