What is the meaning of Selbri?

A word acting like a predicate, which is immediately preceded by one sumti (“argument”), ${\displaystyle x_{1}}$, and usually followed by one or more sumti (“arguments”): ${\displaystyle x_{2}}$, ${\displaystyle x_{3}}$... up to no further than ${\displaystyle x_{5}}$. It is analogous to a verb in natural languages (non-constructed languages).

Source: wiktionary.org