This is another two categories most faeries fall under. Seelie means that they are friendly towards humans. They will help humans when asked and will protect them from harm. The unseelie faeries are obviously the opposite of this. They are more likely to assault or harm travellers or plague humans.
Both solitary faeries and court faeries fall under these categories. Some of the solitary fae that fall under the seelie category would be selkies or leprechauns or brownies. Some that would fall under the unseelie category would be boggarts or nixies or red caps. As for court faeries, there are seelie courts and unseelie courts. The courts are either all seelie or all unseelie, there are not some that have a mix of seelie and unseelie faeries, and of course the seelie and unseelie courts are at war most of the time.