In the rwx symbols used for Linux file or directory permissions, what does the x mean for a directory?

The "x" in the rwx symbols for Linux file or directory permissions stands for "execute".

For a file, this means the file is executable - it can be run as a program.

For a directory, the "x" has a slightly different meaning. It means the directory is "searchable". In practical terms, this means you can access the directory and "cd" into it. If a directory didn't have the "x" permission, you wouldn't be able to access it or see what's inside, even if you had read permission.