A typed feature structure is a record with a type, whose fields can be only partly known, and which you combine with other records by unification instead of overwriting them. Combining keeps everything both sides say and fails if they disagree, so a record can start with what you know now and fill in as more arrives.

The idea comes from computational linguistics, where it was used to build up the meaning of a sentence one piece at a time. In Bondy, a structural shape such as {name: String, age: Int & >= 0} is a typed feature structure, and & is how you combine them.