^This is true. A committee letter is from a premed advisory committee. If your school has a committee process & you don't use it, it does look bad.
The committee letter is not from a committee of people in your department (Azianmunk seems to infer this in an earlier post on this thread). The committee (or the pre-med advisor) generally has access to your AMCAS essay and/or a biographical statement, your grades and other material in your academic file, all letters of recommendation submitted to the office for inclusion along with the committee letter, and the notes take during conversations with the applicant. The letter has a format that is unique to each school but it may include information about your class rank, institutional actions (probation, academic infractions -- usually to say that the record is clean), your high school class rank and SAT scores (rarely included but I've seen it done), your family background, your academic performance, extracurricular activities and interest and brief quotes from the letters of recommendation that you've solicited from faculty. Some will actually tell a story about your journey to medicine if it is something unusual or noteworthy (the post-bach schools are good at this). Some other schools just send a form letter describing the school and the grading policies at the school and giving a break-down of the grading curve at the school and quantifying the student's class rank and gpa. Some also classify students as Most Highly Recommended, Highly recommended, recommended, recommended with reservations, offered for your consideration. Some schools won't tell you that they have a grade higher than "highly recommend" and you only figure it out after you see someone with the "most highly" recommendation. Other schools tell you how many applicants in the previous year's class were in each group and what proportion of each group matriculated at a med school. The admissions offices of the medical schools get to know pre-med adivosrs over the years by style and reputation and many are known and referred to on a first name basis (Kay at Duke, for example). Anyway, as you can see, a committee letter can be very valuable to an adcom and when it is expected, its absence is glaring.