Describes a lack of proper attention or care; often used in the pattern ~をおろそかにする (to neglect something).
See also: おろそかにする
勉強をおろそかにしてはいけない。
You must not neglect your studies.
He was fired because he was negligent in his work.
You mustn't neglect taking care of your health.
Even a small greeting shouldn't be treated carelessly.