The term "seleenwoche" does not appear in standard German, Austrian German, or any recognized German dialect. It has no meaning in Austria or any German-speaking region.
The term might be a misspelling or mishearing of several actual German words:
Austrian German (Österreichisches Deutsch) has distinctive vocabulary (e.g., "Marille" for apricot, "Paradeiser" for tomato, "Jänner" for January), but "seleenwoche" is not among them. Austrian legal, administrative, and educational terminology uses standard German compounds with Austrian variations.
If you encountered this term in a specific context (literature, conversation, document), please provide that context for a more targeted explanation. It may be a proper noun, brand name, typo, or highly specialized jargon.