Acronym for Browser Helper Object.
A Browser Helper Object is a DLL that allows developers to customize and control Internet Explorer. When Internet Explorer starts it reads the registry to locate any installed BHOs and then creates them. Created BHO’s have access to all the events and properties of that browsing session. Every time a new browser window is opened, it creates a copy of the BHO and when that window is closed, it destroys its copy of the BHO.