closed form

Short definition from Wiktionary

Noun

1. 1
   A form (expression) that does not use limits, implicitly or explicitly.
2. 2
   A differential form whose exterior derivative is zero.
3. 3
   A type of poetry with regular structure, such as meter or a rhyming pattern.
4. 4
   Trobar clus.
5. 5
   Used other than figuratively or idiomatically: see closed, form.