Strainer is a course filter. Any device, which removes particles, which are visible to naked eye, the same is known as strainer. Device, which removes particles, which are not, visible to naked eye, the same is known as filter. General rule says that a device, which removes particles coarse than 200 mesh (74 microns) is known as strainer & a device, which removes particles finer than 200 mesh is known as filter.