All words entered in Recoll search fields will be processed for wildcard expansion before the request is finally executed.
The wildcard characters are:
* which matches 0 or more characters.
? which matches a single character.
[] which allow defining sets of characters to be matched (ex: [abc] matches a single character which may be 'a' or 'b' or 'c', [0-9] matches any number.
You should be aware of a few things before using wildcards.
Using a wildcard character at the beginning of a word can make for a slow search because Recoll will have to scan the whole index term list to find the matches.
Using a * at the end of a word can produce more matches than you would think, and strange search results. You can use the term explorer tool to check what completions exist for a given term. You can also see exactly what search was performed by clicking on the link at the top of the result list. In general, for natural language terms, stem expansion will produce better results than an ending * (stem expansion is turned off when any wildcard character appears in the term).