Buddhism is a path leading to ultimate happiness in timeless values.
Every being searches for happiness and wants to avoid suffering. Most things, that we expect happiness from, turn out to be impermanent and ultimatley even lead to further suffering. Buddha noticed this 2500 years. With an immense motivation of wanting to find a way beyond this for all beings, he started his search for ultimate happiness. He achieved a state called "enlightenment", an experience of limitless and permanent happiness. This experience he wanted to make accessible for everyone and started teaching the buddhist path, the path to ultimate happiness.
Buddhism therefore differs from other religions: Buddha wasn't looking for followers, he was looking for colleagues. It is not about believing in enlightenment, but experiencing it oneself. Nothing is done to worship the Buddha, but to develop our own mind.
The meaning of buddhism can not be caught in words like "psychology" or "philosophy". Where psychology brings about changes in relation to yourself and others and thereby reduces problems, buddhism aims at experiencing non-duality: "if I do not ultimately exist, then who exactly has a problem?" Where philosophy provides answers to questions, buddhism delivers methods to find answers to questions.