What is the difference between questionnaire and a survey?

Answer 1

Those two words are synonymous. They are used interchangeably in the literature. In some cases a survey might relate to a questionnaire that is distributed by different modes (paper, telephone, internet) whereas a questionnaire might refer primarily to the paper mode. It isn't always the case however.
A survey is the process of describing some aspect of a population based on a sample. A questionnaire is an instrument used to delve more deeply into the data.

Answer 2

A questionnaire is one of many ways through which a survey can be conducted. A survey can also take the form of a telephone or face to face interview. In some situations the target population is inanimate or otherwise unable to communicate and a survey is simply a way by which the investigator collects information. For example, if you wanted to do a survey of the trees in a park, you would not ask the trees(!) but could simply divide the park into sectors, and count the number of species of different trees in a sample of sectors.

Answer 3

A questionnaire is a set of questions used to gather specific information, while a survey is a method of collecting data from a group of individuals based on those questions. A survey can include various tools and techniques, such as questionnaires, interviews, or observations.