From Wikipedia:
The BMW M3 is a high-performance version
of the BMW 3 Series, developed by BMW's in-house motorsport division,
BMW M GmbH. M3 models have been produced for every generation of 3
Series since the E30 M3 was introduced in 1986.
The
initial model was available in a coupé body style, with a convertible
body style added soon after. M3 Sedans were available during the E36
(1994–1999) and E90 (2008–2012) generations. Since 2014, the M3 has been
solely produced in the sedan body style, due to the coupé and
convertible models being rebranded as the 4 Series range, making the
high-performance variant the M4.
Upgrades over
the regular 3 Series models include engines, handling, brakes,
aerodynamics, lightweight materials and various interior upgrades.