If you're making a quilt out of blocks of one kind or another, the block size will have significant influence on the dimensions of your quilt. You have control over how many blocks you include and in what configuration, of course.
IMHO, any quilt smaller than (or maybe equal to) a twin bed size can be called a lap or throw quilt, depending on how it's used. (A baby quilt, however, would definitely be smaller than a twin bed size.) I wouldn't worry too much about what the "quilt police" might think. Make your quilts lap/throw quilts to whatever size you like. Or customize them according to the needs of the recipient.