What do the tire numbers mean?

In a tire with metric sizing, on an example of 120/70ZR17:

120=tire width in millimeters

70=aspect ratio

Z=speed rating

R=construction type

17=rim diameter in inches

In a tire with alpha numeric sizing, on an example of MT90H16:

M=motorcycle use

T=tire width code

90=aspect ratio

H=speed rating

16=rim diameter