dictionary definition.... "Beam...a long sturdy piece of squared timber or steel used in house building "

For the notes on this site a beam is a structural member considered because it is primarily loaded in a transverse direction to its length..   
A column is a structural member compressively loaded along its length..

A beam is typically a structural member which has a constant section and has a length dimension which is long compared to its section dimensions.   It primarily support loads in a transverse direction to its length.

Beams are primarily used in construction of structures. In mechanical engineering shafts, levers, springs, gear teeth are designed using beam theory..

This section only relates to beams subject to transverse loads, it does not include notes on beams withstanding axial or torsional loads