∝
Symbol  Format  Data 

∝  Code Point 
U+221D 
TeX 
\propto 

SVG 
The proportional symbol indicates that one expression changes in proportion to the other. For example, in the definition of an angle measured in radians, it can be said that the radius is proportional to the arc length.
In plain language, this means that as the radius of the circle grows, the arc length described by an angle also grows proportionally.
The infinity symbol in math represents the concept of infinity. For example, the symbol is used in the notation of a limit to denote that the variable grows arbitrarily large, rather than literally meaning an infinite value.