With more and more people exploring office romances, the line between a business dinner and a romantic date can become blurred. What may appear to be an invitation to an after-hours business dinner or casual group outing may actually turn out to have a more intimate purpose. It's not always easy to tell if a good friend of the opposite sex considers an outing to be a platonic evening out or has romantic intentions. The best way to figure this out is to consider your relationship with the individual and the venue for the get-together. Of course, some people choose to simply ask the person his or her intentions, or trust their instincts.
One thing you may want to consider is the nature of the invitation itself. Sometimes, it is logical to assume a co-worker or fellow classmate may want to discuss a project over a casual dinner. If this person has not demonstrated a romantic interest in you before and the invitation comes about during a business conversation, chances are the planned event is not a date. On the other hand, if you've noticed that person spending more time than usual chatting with you, or he or she has been asking questions about your personal life, then you may want to keep an open mind about the nature of the invitation. Sometimes a person with romantic interest in a co-worker will test the waters through an informal dinner with business overtones.
Sometimes, people will actually be straightforward and explain the nature of the invitation. They will clearly state that the dinner meeting is not a date or there will be others joining the table to discuss the project. There is also no reason why you couldn't clarify any ambiguities about the nature of the meeting. Planning for a romantic evening is a completely different prospect than planning for a business meeting or platonic evening out, so you have every right to ask the inviter if this should be considered a date or not. It may sound like an embarrassing question to ask, especially if the meeting is strictly business-oriented, but it's better to know ahead of time, and avoid misunderstandings later.
You may also want to consider the venue and your financial obligations. An invitation to meet at a local cafeteria to go over sales figures or discuss an advertising campaign is not quite the same as an invitation to dinner at one of the most exclusive restaurants in town. If the inviter asks you to bring specific business items such as reports or files, it would be safe to assume this is not a romantic event. An invitation that seems to be more of a personal nature, such as getting to know a co-worker better, might be considered a testing of the romantic waters, if not exactly a first date. Any offer to pick up the entire bill is usually a signal that the invitee has some form of romantic intent. When in doubt, it's best to ask the inviter discreetly about the arrangements before ordering an expensive meal or extras such as alcohol or dessert. Unless you know for certain the other party is footing the bill, order within your own budget to avoid confusion later.
Many people who have been in the dating scene long enough learn to recognize the difference between a casual meeting and a romantic one, so you may just want to trust your instincts. If the person seems interested in getting to know you as a person rather than as a colleague, makes an effort to minimize interruptions while having dinner with you, or has shown an interest in doing other activities with you in the future, then it's most likely a real date and you should feel free to act accordingly.