A student information system (SIS) is the software that holds the record of every student in a school, college or university: admission, attendance, timetable, marks, fees and the final transcript. A transcript is the official list of every subject that a student took, with the grade in each. The college portal, where students check their attendance and download hall tickets, mostly shows data from the SIS. In India, the SIS is often sold as part of a "college ERP".
The SIS is the institution's system of record. Many other systems keep copies of student data, but the SIS holds the official version. If the hostel system and the SIS disagree about a student's name or roll number, the SIS is taken as correct.
Here is a typical case. An engineering college in Hubballi admits 720 students to its first year. Each admitted student's details arrive from the admissions management software. The SIS gives each student a roll number, and places each one in a section and in the timetable. Teachers mark attendance in each lecture on a phone app. Every week, the SIS calculates each student's attendance in each subject. Say one student has attended 41 of 56 Physics lectures, which is 73%. The college requires 75% to sit the exam. So the SIS warns the student and the class mentor three weeks before the exam, while there is still time to attend the remaining lectures.
In the same semester, the SIS records the internal marks that teachers enter, and the fee payments. A student pays the semester fee through a payment gateway, and the gateway tells the SIS that the payment succeeded. The SIS then marks the fee as paid. Before the exams, it issues a hall ticket only to students who have paid their fees and met the attendance rule. After the results, it produces each student's grade sheet.
In India, the SIS also connects to national systems. Each student has an APAAR ID, a lifelong 12-digit student ID. The SIS uploads the credits that each student earns to the Academic Bank of Credits (ABC). With ABC, a student who moves to another university can take the earned credits along. Final marksheets and degrees are uploaded to DigiLocker, so that an employer can check them online.
The SIS sends course lists to the learning management system (LMS), so that each student sees the right courses. It sends the fees it has collected to the university ERP, which keeps the accounts.
The largest SIS companies sell mainly to school districts and universities in the United States, and several of them build their products in Bengaluru and Chennai. Replacing an SIS is slow and risky, for the same reason that replacing a bank's core system is: decades of records must move to the new system without a single mark going wrong.