Earnings per share (EPS) is the earnings returned on the amount invested initially.
EPS is calculated as bottom line net income divided by the number of shares outstanding.
The value used for company earnings can either be the last twelve months' Net income (referred to as trailing-twelve-months, or ttm), or analysts' predictions for the next twelve months' net income (referred to as forward).
The number of shares used for the calculation can either be basic (only shares that are currently outstanding) or diluted (includes all shares that could potentially enter the market).