Most positions are never advertised. A cold cover letter is an uninvited inquiry to an employer, recruiter or other hiring manager regarding possible job .
A cover letter is a letter you send with your resume when applying to a specific job at a specific time (when they ask for job applications and/or post an opening). A letter of interest can be sent at any time whether or not the company is actively hiring and isn't sent in response to a specific job opening.
When looking for a new job, you may find that some companies you are interested in. How to Write a Cover Letter to a Company That Does Not Have a Job Opening. If you are sending a hard copy of the cover letter, put your name and contact information on. If you are willing to relocate, let the potential employer know.