A more thorough explanation:

The doctrine of substantial equivalents is a legal theory used in patent law to determine if a product or process infringes on a patent, even if it falls outside the literal scope of the patent claims. This doctrine was created to prevent parties from avoiding liability for patent infringement by making minor changes to the product or process to avoid the language of the patent claims.

For example, if a patent claims a product with a specific element, and another product has a similar element that performs the same function in the same way to achieve the same result, it may be considered an infringement under the doctrine of substantial equivalents.

However, prosecution-history estoppel may limit the use of this doctrine if the patentee voluntarily amended the claim. On the other hand, the reverse doctrine of equivalents may prevent infringement liability if the invention is substantially described by the claims of another's patent but performs the same or similar function in a substantially different way.