Almost always paired with strong adjectives: 严明 ('strict and clear'), 严格 ('rigorous'), or, negatively, 松弛 ('lax') and 涣散 ('disorganized'). 整顿军纪 ('to tighten military discipline') is a stock phrase in news about reforms and crackdowns.
memory
军 'army' + 纪 'rules / chronicle' (the same 纪 as in 纪律 'discipline'). Compose any group with 纪 and you get 'rules of that group': 校纪 school discipline, 党纪 party discipline.
