Karma sannyasa is a special philosophy in a yogic lifestyle, and is considered a form of renunciation among many traditional schools of yoga.
Unlike most forms of renunciation, the external life continues as it is. You live with your family, go to work, go shopping, go on holidays, all of that.
The changes are internal and they are many, large and gradual.
Karma sannyasa is "inaction in action". The main focus is that there is no problem in action, but the danger lies in attachment and dependence on the fruits of the actions you have performed.
The idea is to live life fully, participate in all events of life externally, but internally maintain the attitude of non-doership.
It is believed that if a person can understand and implement this concept, that they will slowly experience a higher quality of life.
Swami Satyananda Saraswati comments on Karma Sannyasa:
"Karma sannyasa is more difficult to maintain than full sannyasa, because at times it can be very difficult for the disciple to maintain a balance between his worldly life and his inner life. Sometimes he may lean too heaviliy towards his inner life and neglect his duties towards his family; at other times he may get caught up in the maya of worldly life and its distractions, and his sadhana may suffer. A karma sannyasin has to be very careful of this point. He should strive to maintain a balance."