Question: what does the ar in ar 15 mean
[{'answer': 'ArmaLite Rifle', 'provenance': [{'wikipedia_id': '37903544', 'title': 'AR-15 style rifle', 'start_paragraph_id': 4, 'start_character': 101, 'end_paragraph_id': 4, 'end_character': 115, 'bleu_score': 1.0, 'section': 'Section::::Terminology.\n'}]}, {'provenance': [{'wikipedia_id': '37903544', 'title': 'AR-15 style rifle', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 693, 'bleu_score': 0.707617907612565, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4957907045734538719}, 'section': 'Section::::Terminology.\n'}]}]