# What does it mean to say that a language is “effectively closed” under an operation?

I've been reading some formal language theory papers, and I've come across a term that I don't understand.

The paper will often refer to a set being "effectively closed under intersection" or other operations. What does "effectively" mean here? How does this differ from normal closure?

For reference, the paper I'm seeing these in is:

M. Daley and I. McQuillan. Formal modelling of viral gene compression. International Journal of Foundations of Computer Science, 16(3):453–469, 2005.

Then it is a natural question, whether there are examples of closure properties that are not effective. I know one right now. For a regular language $R$ and any language $L$ the quotient $R/L$ is again regular. There is no effective way to construct a FSA for that quotient if $L$ is e.g. recursively enumarable.