I used to use WingIde, where in a shortcut(f4, default) which I used quite often was Goto definition, which will open the definition file, and take me to it. Is the         
        
As others answered, F3 is the way to go, but going a bit further, you might also want to take a look at ctrl+shift+t to browse all the tokens available and ctrl+shift+r to browse all the files.
Actually it does not work when you set MSVC scheme. In eclipse mars go to
Windows->preferences then go to General->keys (or in type filter text type keys) then in Keys in type filter text type definition. Then you shall see in command below Python Go To Definition. In Binding text edit you can then set any shortcut you want.
For Aptana Pydev, you have "Go To Definition": F3
(Andrew Falanga comments below that Alt+← allows you to return to the point you left)
The 'go to definition' actions enables you to get to a given definition.
- It works well on 'self' tokens
- It can work on methods / attributes from parameters (as the image below shows).

Although the question is pretty time-barred, maybe this more general approach will help others looking for specific short-cuts in eclipse.
Help - Key Assist... opens a list of all available short-cuts, alphabetically sorted by description. ("Open Declaration" was the one looked for here.)
Window - Preferences - General - Keys lets you edit the short-cuts.
Assuming you mean "go to where a method/class/variable" is defined, in Eclipse, it is F3