Integer and array types which are used by—but not unique to—Ethereum.

Uint represents non-negative integers of arbitrary size, while subclasses of FixedUnsigned (like U256 or U32) represent non-negative integers of particular sizes.

Similarly, Bytes represents arbitrarily long byte sequences, while subclasses of FixedBytes (like Bytes0 or Bytes64) represent sequences containing an exact number of bytes.