Sorry, I won´t give you are textbook definition of the term. There are different variations of this term (e.g. biopsycho-socio or bio-psychosocial) and the cultural aspect is not very often mentioned...
This expression tries to describe the different aspects and influences of any psychological / psychiatric problem.
BIO = biological is the somatic or biological caused vulnerability or diathesis. Each of us is an individual. There can be some organic differences which could be defined by examination or special tests. Usually the biological origin is not defined but the expert expects each individual to show individual response to its world or to have different levels of the neurotransmitters in the brain. This biological model of psychiatric disorders is very popular to explain depression or schizophrenia. It tries to express the fact that some people are more prone to a psychiatric disorder than others. However anyone might develop a depression or schizophrenia, if the psychological stress is severe. This is also called the diathesis-stress model of psychological disorders.
Psycho = Psychological
Any type of change or new demand may cause stress to a person. Stress is a rather unspecific reaction of the body to any kind of demand (not only much work or crying children). Any kind of situation which is new or threatening for us may cause a (biological) alarm reaction.
However severe psychological stress events are more likely to cause problem than a short, mild or well-known situation. It depends on your personal life and experiences (e.g. bad experiences in the past), deficits of learned behaviour or skills or coping abilities (how you are able to handle stress or problems of everyday life).
These psychological issues can contribute to the development and course of a psychiatric disorder.
Social : Any psychological problem depends on the social interaction and response of the environment. So it makes a big difference where and how you live. If you are alone it is much harder to cope with depressive thoughts or chronic pain. To be connected to a supportive family would help you to handle any emotional stress and desperation. However, ongoing problems in the family may be a reason for problems.
Cultural: This is not always considered in the model. Web4Health is a rather interesting example of multicultural psychology. We are European psychotherapists. Most of our readers might be living in different societies. It makes a big difference to give advice to an European women or to an Indian girl. Even within a country or region there might be different norms or religious influences. All this may contribute to the problem...
So this is my short description of the term... I hope it helps. Maybe your child gives a very personal description which is much more appropriate. Do not hesitate to post it to me and I will be glad to publish any better definition here :-)