Usually light-colored, low temperature, minerals that are rich in feldspars (hence fel} and silicas (hence sic) (Isn't philology fun?) They melt/crystallize at relatively low temperatures (900° - 500° C}. Common felsic minerals are quartz, feldspars, and muscovite micas.
The term also refers to rocks that are high in felsic minerals, also generally light-colored, such as granite and rhyolite.
Because felsic minerals melt at lower temperatures, felsic magmas usually form at subduction zones where water-rich sedimentary rocks are pushed into the mantle and melted. Also because of the low temperatures, felsic lavas are generally very viscous and felsic volcanoes tend toward lava plugs, ash falls and pyroclastic flows rather than lava flows and fountains.