Weird message from my host, any idea what ps aux|grep means?

My host tells me that my WordPress 2.7.1 site is overloading the server.

They told me this, and I don’t really recognize the language (not php, css, html…). What is he talking about?? Is this anything to do with my WP?

– Please use “ps aux|grep username” instead of “ps -aux|grep username” and you will not face Bad syntax message.

any ideas how to fix this?

Next he said this,

I do recommend you to ask your webmaster to provide you with more details.

of course, I am the webmaster, now in need of advice