This is one translation of the word Dukkha but it's actually much more general.

Indeed before he became enlightened, according to the sutras, Buddha learnt to enter states of mind even beyond perception and non perception, refined states with not a trace of suffering in the ordinary sense.

However having mastered those meditations, and even asked by his second teacher to take over from him as teacher of that meditation technique, he decided that this was not what he was looking for.

The reason is that these refined states were still dependent on conditions. It was believed at the time that even after death, that these refined states would continue, perhaps for immense periods of time, but still, that was not enough. Even if they lasted for many times the age of the universe, with not a trace of suffering at all for all that time, it would not be a final answer to the problem of dukkha - suffering or unsatisfactoriness, because eventually you are still dependent on conditioned existence, impermanent changing things.

So the idea of dukkha is subtle. Life is full of dukkha in this sense, even if you are in a state of bliss and happiness for years on end without any suffering and even without any anxiety and without any problems or worries at all.

And then in the four noble truths he taught that there is a path that leads to cessation of this unsatisfactoriness. Which is basically to do with relating directly to the impermanent and changing nature of things, and also of oneself.

He said that if you do that, then you can come to see a truth that has to be experienced. And once you see that truth, you are then liberated from this dukkha, unsatisfactoriness. Things are still impermanent, you also are continually changing, you will still get old, you will die. And you don't cease to exist at that moment or get displaced into some other realm, or enter a state of blissful meditation cut off from the world, or anything like that.  But by relating directly to everything just as it is, yourself also, then you waken up and realize this truth and see through all the causes of dukkha.

Those who choose to follow the path of the Buddha believe that there is such a truth to be seen / experienced / discovered.

Some Buddhists will dedicate their lives to seeing this truth, as the Buddha did. Others though will follow the path in other ways, for instance by practicing generosity, loving kindness, compassion, by restraining their conduct, such as lying, stealing, killing etc and in other ways. These also are ways of relating more directly and authentically with the world and ourselves.

Or they may do acts of devotion, or support the Buddhist monks and nuns in traditional Buddhist countries.

So, it's not at all that all Buddhists are trying to see this truth for themselves, many may not even meditate in their life. But if you are a Buddhist, this is the central idea that you recognize. Not a creed or belief system. But a faith that there is a truth to be discovered of this nature, and one that needs to be experienced directly rather than just understood intellectually. And you don't need to be an intellectual or clever to see it. It's said to be a truth that is blindingly obvious if only one could wake up, that we continually miss this truth because it is so obvious rather than because it is difficult to see. A bit like the way you may miss the largest letters on a map.

For more about this, see The Decision to Become a Buddhist by Trungpa Rinpoche