When a person is "in the swim," he is at the center of action and up-to-date with the latest information and trends. This person can often be referred to as being in the swim about a certain field of knowledge or business. Generally, this means that important and breaking information and decisions reach him before they reach other people who are less central to the scene. This phrase is also similar to "in the loop" and "in the mix." A less common similar phrase is "in the soup."
Another way people use the phrase is to say they are "in the swim of things," which is a take off on the common idiom "in the swing of things" with a slightly different meaning. The phrase "in the swing of things" refers to a state of proficiency and performance at a task that seems natural and rhythmic. If a worker has been out of the office for a while, she may say that it might take her a while to get back into the swing of things.
When someone says they are "in the swim of things," it is the same as saying that they are "in the swim," or that they are back into the circle of communication and activity. If a person has not been part of something for a while, he may be out of the swim of things. A similar idiom to "in the swim" might be "in the loop," a phrase that indicates a person is in the center of involvement or communication about a certain project or topic of conversation. Someone who has not been included in the central communication circle for a piece of information or topic might be said to be out of the loop.
Both phrases can be used in many settings, including business and personal relationships. If a teenager has not heard about an exciting piece of gossip from her friends, she might say she was left out of the loop. A worker at a corporation who was not included in the email list for a discussion might also say he was not in the swim or not in the loop for the discussion topic. In business, a person who is competing with another person for a job might say the other person is not "in the swim," meaning the competitor has a deficiency of involvement and contacts within the field of business. It would imply that the competitor is not connected within the business world and lacks the proper channels for communication.