Earnings per share is the total profit that a company made divided up among the ownership units (shares). EPS is reported quarterly and is calculated by dividing the net income (earnings) for the quarter by the number of shares outstanding during that quarter.
The trailing EPS is the sum of earnings per share (EPS) from the last four quarters. It is with trailing EPS that most price to earnings ratios (P/Es) are computed.
You can find trailing EPS values on the Fool Website. Just plug in a ticker symbol in the white box in the upper left column which takes you to the Quotes page. Then look for a link to the Financials page on the right side of the Quotes page. That's where you'll get the trailing EPS data.