Code reuse is the practice of using existing source code to develop software instead of writing new code. Software reuse is a broader term that implies using any existing software asset to develop software instead of developing it again. An asset that is relatively easy to reuse and offers significant value is considered to have high reusability.
Code reuse may be achieved different ways depending on a complexity of a programming language chosen and range from a lower-level approaches like code copy-pasting (e.g. via snippets), simple functions (procedures or subroutines) or a bunch of objects or functions organized into modules (e.g. libraries) or custom namespaces, and packages, frameworks or software suites in higher-levels.