A standard room is normally the lowest-price room the hotel offers. It might also be described as a Hilton bedroom, a guestroom, or something else. In the Hilton Orchard Road in Singapore, the standard room is called a deluxe room.
In most, but not all, cases, the standard room will offer the choice of a double/queen/king room or a twin/two double room, depending on the hotel. (Two doubles seems to be a popular room offering in North America, less so elsewhere.)