Key-words allow people to search through profiles, looking for things you have in common. It's also a good way to mention all the random things that you didn't write into your profile because they are unrelated to each other, and would disturb the flow of your prose! Your keywords can be searched by other people, and will appear below your profile.

If you have keywords in common, they will be highlighted in bold. Please enter keywords and phrases separated by commas. (The order is unimportant: the keywords will be sorted alphabetically). For example: "raindrops, roses, kittens, copper kettles, warm wollen mittens, brown paper packages, string".

Keywords are also searchable, so, for example, if your profile mentions that you like cats, include 'cat' as a keyword too. It's OK to duplicate information.
The Keyword comparison is quite clever: it knows that 'kitten' and 'kittens' are the same, and that a 'Dog' is also a 'dog'. But it doesn't know that an 'Echidna' is similar to a 'Hedgehog', nor that if you 'skydive', you have survived the experience of 'skydiving'.
When you view your own profile, you will notice that all your keywords are in bold, because you (the viewer) have keywords which all match yourself (the profile).