IEPs are at the heart of special education. An IEP is both the Individual Education Program created for a student with disabilities and the name of the document that describes the plan.
A student with a disability is entitled to an education program tailored to their needs. Some students might need only a little support to access the curriculum while others might need significant support.
The IEP document spells out exactly what supports the student will be getting and in what environment they will be getting that help. So student A might get help in a small group for reading and help in his general education classroom for math while student B might get help in her class for math only.
At least once a year, families and the school come together to share progress and to make a new plan. At that time, they set goals for the student for the coming year and discuss how they will help the student meet those goals.
There are many different types of IEPs and different people required to attend the meetings. To learn more about IEPs, read this article about IEPs and all of the legal requirements.