What do lazy and greedy regular expressions mean?

Greedy expression tries to get as much as possible.
If you write a regular expression like this

<.+>

for the string:

<p>My expression</p>

you will get all the string

<p>My expression</p>

Oh, yes.. this thing is really greedy.

Let's take a look at the lazy one. If you write a regular expression like

<.+?>

We have just added "?". That means we want the smallest possible group. Now we have this result:

<p>

Here you are. The laziest thing you have ever seen :)