What does it mean when the say someones being served. in legal terms?

Do you mean SUMMONS being served? If so, that's when the papers telling you have to go to a court are given to you.

If not.its the main course at the cannibal dinner fest
Depends. It normally means 'To be given'
i.e Served a notice of eviction./ Given a notice of eviction.

It means that notices of various kinds are being delivered to them in such a manner that the court can be satisfied that they have been received by the person concerned. This can take several forms: registered mail, recorded delivery or personal service. In some circumstances service is acceptable if the notice concerned is put through the letter box of the person's last known address or even nailed to their property.
It means a legal notice. The court is telling you
you need to do something.
It means that a solicitor(lawyer) has given them papers to say they are being sued.
it means..time to get a lawyer
When any action is filed in court, all parties to that action have the legal right to know, in advance, the follwing information:
1) Notice of date and time of proceedings (when)
2) Nature and factual basis of filing (why)
3) The name of the entity making the filing (who)
4) The location to which you should report in order to make an answer, i.e. the courthouse (where); and
5) The requested plan designed to remdiate the situation (what)

The court is not allowed to proceed unless all parties have been properly served with all of the above information (service). Most service requires that parties be handed a copy of the above information (personal service). But it can also include registered mailings (service by certified mail), postings at the home (residential service), or even by placing information in the newspaper (service by publication).
to be served with divorce papers, a sommons or other legal documents that must be hand delivered and given only to you
served as in 'a given order' served by the courts///jury duty, appear in court...basically a given order.
it means one has been given papers by the court