The full form of IJP is Internal Job Posting.

An internal job posting is an open job that is available to current employees within the company they work for. Many companies and government departments post jobs internally to promote growth within current employees. Members who already work within a business typically know more about the policies and workplace environment, lowering the training time that would be required if the company hired an external employee. 

The internal application process is typically slightly different than if you applied to an external posting. You will most likely still need to submit an application and prepare for an interview, though the questions that the hiring manager asks may vary from what you would encounter in an external interview. It is important to be ready for the internal hiring process so you appear professional in every step and demonstrate yourself as the strongest candidate for the job.