Wood routers are categorized by the way the motor is attached to the base:
You can use both types of wood router (plunge and fixed-base) in either of two modes: handheld or mounted upside down in a router table. This is more or less like the difference between using a circular saw and a table saw, or a jigsaw versus a scroll saw. In one mode, you hold the wood steady while moving the tool; in the other, you hold the tool steady while moving the wood.
Expert reviews find that within each type, the best handheld router is usually not the very best choice for use with a router table -- so it's a good idea to think ahead about how you are most likely to use a router. Handheld routers are useful for a variety of tasks -- for example: rounding the edges of wood, making grooves, trimming laminate or cutting mortises for hinges. Table-mounted wood routers are used for precise cuts (as for joinery) and production runs.
Although experts say to take horsepower and even current draw (amp) specifications with a grain of salt, router size is specified in horsepower and type. Trim routers, which are rated at one horsepower or less, are best for small jobs. Mid-size routers of 1.75 to 2.25 horsepower (or 10 to 13 amps) are best for general use. Router combo kits are usually of this size. Heavy-duty routers are meant for continuous use or making deep grooves in hard woods. These are usually 3-hp (15-amp) routers.