Microsystem is the name commonly used in Europe to describe the same technology which goes under the name MEMS (Micro Electro Mechanical Systems) in the US. In Japan, this field is often termed micromachines.
Microsystems are miniaturized (silicon or polymer) devices which perform non-electronic functions: typically sensing and actuation. Typical microsystems have mechanical parts, like microbridges in RF switches or bending cantilevers in atomic force microscopes (AFMs); electrical parts like piezoresistors in airbag sensors or capacitors in pressure sensors; or thermal, optical and fluidic structures like heaters and nozzles in inkjet printer or flow sensors.
In biomicrosystems (BioMEMS) cells or microbeads are handled by fluidic streams, magnetic and electric fields, thermal gradients etc. In chemical microsystems operations like sample pretreatment, separation and detection are built on microchips.
This field is also known as microfluidics or lab-on-a-chip. Today it is possible to build up microsystems without any tooling needed by computer-aided direct parallel batch processing technologies called RMPD Rapid Micro Product Development.