According to Wikipedia, "Personal branding, self-branding, self-positioning and all individual branding by whatever name, was first introduced in the 1980 book: "Positioning: The Battle for your Mind", by Al Ries and Jack Trout."
Because the terminalogy is 30 years old and has become jargon doesn't mean it isn't important to your job search or career advancement.
Pesonal branding means taking responsibility for figuring out what you're good at then positioning yourself to demonstrate in writing (cover letter & resume) and in person (interview) how what you're good at can be of use to the employer to whom you are trying to sell yourself.
Unfortunately, lot of current job seekers are under the mistaken impression that it is an employer's responsibility to discover how they should fit into the employer's organization. What a waste (of their time and your opportunity)!
An employer who is trying to fill an opening doesn't have the time to spend figuring out how your indirect experience might relate to the job they need filled yesterday. But if you can take the time to demonstrate how what you've done in the past and how you aproach work can be used to their advantage, you will separate yourself from the multitude of candidates who simply spray and pray.
When you treat job hunting like the lottery, you're limited to luck. When you treat it like a brand (by taking the time to know what you actually have of value to sell to an employer), you should soon start discovering which employers actually need what you have to offer and you'll stop "carrying coal to Newcastle" (where they have plenty already) and start carting it to Wisconsin in the winter where it's sorely needed.