A "survey" is a set of questions that you ask to get some general information about a group of people. Companies often use surveys to find out whether their customers are satisfied. For example, after renting a car the car rental company might email you a survey to ask you questions like "How satisfied were you with our customer service?"
The phrase "take a survey" describes someone answering the questions on a survey:
After the convention, they send you an email asking you to take a survey.
You might also use the phrase "take a survey of ___" to talk about the company or organization who's giving a survey to people.
We took a survey of home shoppers in the Atlanta area to determine what features and amenities were most important to them.