M91 or M-91 may refer to:
* Various iterations of the
Carcano
Carcano, Mannlicher-Carcano, Carcano-Mannlicher, and Mauser-Parravicino, are frequently used names for a series of Italian bolt-action, internal box magazine fed, repeating military rifles and carbines. Introduced in 1891, the rifle was officia ...
, an Italian rifle
*
M-91 (Michigan highway)
M-91 is a largely north–south state trunkline highway in the Lower Peninsula of the US state of Michigan. It runs from Belding to south of Lakeview. Its length exists entirely within Ionia and Montcalm counties. It is all undivided surf ...
, a state highway in Michigan
* M91 rocket launcher, a 115mm, 45-tube, trailer mount for the
M55 rocket used by the United States Army and United States Marine Corps
*
McCarthy 91 function
The McCarthy 91 function is a recursive function, defined by the computer scientist John McCarthy as a test case for formal verification within computer science.
The McCarthy 91 function is defined as
:M(n)=\begin
n - 10, & \mboxn > 100\mbox \ ...
, a recursive function defined by the computer scientist John McCarthy as a test case for formal verification within computer science
*
Messier 91, a barred spiral galaxy about 63 million light-years away in the constellation Coma Berenices
*
Mosin Nagant Model 1891 Infantry Rifle, a Russian/Soviet rifle
* ''
Psihološko propagandni komplet M-91'', the third studio album released in 1991 by Montenegrin-Serbian musician Rambo Amadeus
*
Zastava M91, a Serbian sniper rifle
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