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.
Nation and Macalister, Language Curriculum Design, Routledge
(Don't forget that you can often find used copies of the books you want on Anmazopn at prices well below the original price. it's always worth checking.)