The academic term is very simply how long does each class last. There are many variations of this from college to college
One of the most common terms is the semester. Typically with a semester system classes run for about 15 weeks with one semester in the fall and one in the spring. Students will commonly take four classes each semester. A year long class will last two semesters.
Another option is the quarter system where students will have three 10 week terms. A year long class will last three quarters. Because each quarter is shorter than under the semester system, you don’t have as long between mid terms and finals but you have each three times a year rather than two. The number of classes will vary depending on the intensity of each class.
Another common option, particularly among small liberal arts colleges is the 4-1-4 system. This is similar to the semester system with two longer terms of roughly four months. Again, you would typically take four classes each term. Between those two terms is a one month term, typically in January, where you take one class and one class only for the month. These are often classes in unusual topics that the professor wants to teach. Many of the colleges with this type of system also allow students to do other things during the one month January term such as internships or self directed classes.
But there are still more options. A few colleges have what is known as the trimester system where students have three ten week sessions. While this may look like a quarter system it is quite different because each 10 week term covers half a year of a full year class. This means that after two trimesters, you will have completed an entire year long course. Because classes are accelerated in this type of system, students typically only take three classes each term. Although only having to take three classes may sound like you will have lots of free time, colleges on this system are covering so much material in each class that you will be working hard to keep up. As a bonus, you will take at least nine courses a year rather than the eight typically taken in a quarter or semester system.
Finally, there are a few colleges with a block system. With a block system you take one course at a time and it lasts about three and a half weeks. But since you are only taking one class at a time, you are very focused on that one class for those three weeks. These colleges typically have eight blocks during the year so you end up taking a total of eight classes each year.
Does it matter to medical schools what type of academic year your college has? No. But you should find one that meets your particular interests and needs.