An ELT Glossary : Beginner / True beginner / False beginner
The term beginner covers learners working towards CEFR Level A1 - ie learners who are still developing a basic command of the language, familiarity with everyday expressions and the ability to construct simple sentences.
A true beginner is a learner who is starting to learn a language from scratch - ie they have never studied the language before.
Many learners who are placed in beginners' classes are not, however, in that situation. They are learners who do have some knowledge of the language - for example because they studied it many years before. These are commonly called false beginners.
In a private language school, the composition of a beginners' class will often be a mixture of the two types of beginner. This can sometimes cause problems as their rates of progress may be different : the false beginners only need to reactivate language that they previously knew, and may find it easier to assimilate the material covered on the course. This may be demotivating for the true beginners if they do not understand why they seem to have more difficulty than other students with the language.