Abstract: A trimmer and a trimmer head include an upper cover assembly being connected to and driven by a motor, wherein the upper cover assembly is configured to be removably connected to at least one of a first trimming assembly or a second trimming assembly selectively, and is provided with at least one connection hole in its side wall; the first trimming assembly is configured to include a first lower cover, a first cutting member, and a first base; the second trimming assembly is configured to include a second lower cover, a second cutting member, and a second base; wherein the first base is at least partially inserted into the connection hole when the first trimming assembly is mounted, and the second lower cover is at least partially inserted into the connection hole when the second trimming assembly is mounted.