bolt-on meaning

adjective
  Additional, supplementary
  noun
  An additional part which can be attached to a computer or other machine

[Business]
adjective [only before noun]

something that can be easily added to a machine, a website, a company, etc. to enable it to do sth new:

They have added bolt-on e-commerce software to their website to enable customers to order direct.

The company has expanded its software range through a series of bolt-on acquisitions (= by buying small companies that make different software products).