From OpenCog

Deprecated -- you should probably use PutLink combined with DeleteLink instead. PutLink is more flexible and is .. prettier.

The RemoveLink allows a Link to be described, in such a way that the description is in the AtomSpace, but the Link itself is need not be. The link it describes is not removed until the RemoveLink is executed with the cog-execute! function, or with the pattern matcher.

The RemoveLink is paired with the InsertLink, which describes a link to be inserted when it is executed. These two are roughly analogous to the Prolog concept of "assert" and "retract". The AssignLink combines the two into one, behaving like the assignment operator (viz the = sign in C++, python, perl) in procedural programming languages.

InsertLink, RemoveLink and AssignLink have the form of a special case of a SignatureLink.

The DeleteLink provides a different format for specifying links to be removed from the AtomSpace.