An online certificate is similar to an online degree, though a certificate earns you certification and training to work in a specific technical field.
Certification usually allows you to be hired in specific technical fields like aviation, technology, health care, industrial sectors, and finance.
Certificate programs are offered by a professional society, not the government. This means at the time of completion you are given a certificate of completion, and not an advance degree such as an Associate of Arts or a Bachelors degree.
Certificates often expire, and require ongoing education and certification, though this is not always the case. Some professions simply make you retest for the specific field you're working in.
One key benefit of certificate programs is that you're trained by a professional in the field to work in that specific field. This means that if you've earned a certificate in graphic design, the goal is that you graduate with the tools and hands-on know how to be a graphic designer.
Aside from general certification programs there is also corporate certification, which is used internally by a company to train employees of their specific procedures or workings. There is also product-specific certification to train individuals to use specific pieces of hardware and software.