Mach Number

The ratio of true airspeed to the speed of sound in the same atmospheric conditions; e.g., MACH .82, MACH 1.6. Named in honor of Ernst Mach, late 19th century physicist.

Source: 14 CFR Federal Aviation Regulations §1, PCG, Pilot Handbook of Aeronatical Knowledge

See:

#
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z