type of primary election in which previously unaffiliated voters may participate in the partisan primary of their choice. Voters who are already affiliated with a political party can vote only in that party's primary.

https://ballotpedia.org/Semi-closed_primary

I use ballotpedia, too. I looked it up. I just wondered if we were talking about the same thing.

We have an open primary in Illinois. I think all primaries should be closed.

I would think that a semi-closed primary could cause a lot of extra work for election judges. It can be hard to recruit judges as it is.