An ELT Glossary : A-Priori Syllabus / A-Posteriori Syllabus
An a-priori syllabus is one which is designed before the course is taught, and uses selected materials and activities achieve the previously determined objectives. Any course following a coursebook will have an a-priori syllabus.
An a-posteriori syllabus is one which is not predetermined but emerges from the course itself - as the course progresses the teacher will note what has been covered and, at the end of the course, could use this as a record of what has been achieved, or if necessary to design an end of course test. A course following the principles of Community Language Learning or Dogme could have an a-posteriori syllabus.