Well having a brand means that you have a logo and a name or a mark that people will know you for. It's something that you use to get your content out there and for others to identify who you are. It's like people will immediately know what that is when they see your brand. For example, my logo and name is a part of my branding. People know me for the stylings of my name and for the logo that I use for my avatars, music albums, etc. To better get a brand out there, not only in videos, but people use their brands in merchandise, like stickers, shirts, hoodies, etc. Another example is that I have my own stickers and wristbands that have my branding on them. This is what people generally mean.