Linear algebraic group
In terms of underlying variety
By a basic theorem of algebraic geometry, any affine algebraic geometry has a faithful linear representation, and can hence be realized as a linear algebraic group. Thus, we often view affine algebraic group and linear algebraic group as synonyms.
In terms of embedding into general linear group
A linear algebraic group or affine algebraic group over a field is defined as an algebraic group such that there exists an embedding of as a closed subgroup of the general linear group for some choice of (and this embedding is a morphism of algebraic varieties).
Note that such an embedding as a closed subgroup of automatically gives an algebraic group structure, so if we provide an embedding, we do not need to specify an algebraic group structure separately. This is because comes naturally equipped with an algebraic group structure, and any closed subgroup of algebraic group inherits algebraic group structure.