As far as I know there are only locigal conditions and wildcards.
Maybe if you have a description like This is my test-ticket you can search for it with something like *test*. This works like if you use the SQL-Statement LIKE with a front and a back %. So test* would not find the example as it does not start with test. Same with *test as there are characters behind it.
If you have whitespace in your search you have to put it into double quotes ( ") like this: "*my test*"
And then you can combine those terms with and, or, (, ), NOT, <, >, <=, >=, = (see list in the select filter condition dialog).
As far as I know there are not more regExs but I'm not sure. I didn't find anything in the documentation about it.