The verb matsu (待つ) means to wait. A simple phrase that you can say to someone in a situation where someone needs to wait is chotto matte (ちょっと待って). Chotto means a little bit. If you want to make this more polite you can add kudasai to the end.
Omatase shimashita (お待たせしました)
Omatase shimashita ( お待たせしました) is a polite phrase that is used to apologize for making someone else wait for you. In English it means something close to,
● I'm sorry to keep you waiting
● I've made you wait
Often when you go to pay for your item at a store clerks will say the more formal phrase, omataseitashimashita (お待たせいたしました). They often will say this even if you did not wait in line for a long time at all. This is simply a way to be polite. In casual situations with your friends you can say omatase (お待たせ).