P/E is a ratio that compares the current market price of a security to the earnings per share. It is calculated as:
Market price per share / Earnings per share
Earnings per share = Profit after tax / Number of shares outstanding
P/E and PE are often used interchangeably when talking about stocks and they mean one and the same - Price to earnings ratio. Alternatively, CE and PE in the context of Options mean European Call and European Put option, respectively.