The amplification of light from stars, sometimes called ``microlensing'', was proposed by Paczynski (1986) as a means to detect MAssive Compact Halo Objects (MACHOs). This prediction of photometric lensing events in the light from stars in the large Magellanic Cloud (LMC) was confirmed by Alcock et al. (1993) and Aubourg et al. (1993) through their detection of three events, probably caused by MACHOs of about solar masses as they passed within less than one milliarcsecond (mas) of the line-of-sight to a star. Nine lensing events in the light from stars in the Galactic bulge have been reported by Udalski et al. (1993, 1994) and pacz94 with characteristic times between 8.6 and 62 days.
The acronym MACHO has a very precise meaning in itself, but it has become a mis-nomer since it is still attached to all objects discovered by observation of microlensing, even though many of these are ordinary low-mass dwarfs, according to pacz94. This is the case for many MACHOs discovered in the direction of the Galactic bulge. MACHO is also the name of one of the collaborations searching for microlensing, i.e., Alcock et al.