my 2 cents...
I think most of people consider as Trend the tendency of data to be on a pattern they believe to see in the data.
Trend is not objective, but mostly subjective.
Simpler patterns tend to be considered more "objective" by people, then more complex ones.
Again the degree of complexity of a pattern may depend on subjective factors and on education.
Whatever trend is, the concept is probably not crucial for trading because even if you see a trend you can conclude in several ways:
- There is a trend: good it will probably continue!
- There is a trend: ah things have gone too long according that pattern, now they are going to change !
and whatever you conclude, the market is always able to find the ways to disprove you

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Anyway trends do have some significance. If a price is going up and you go short, if you eventually lose many people would feel entitled to tell you acted in a stupid way.
On the other end if you went long and the direction reversed after 30 seconds, well it would more difficult to blame you for your decision.
So, trend probably does not exists, but it cannot be ignored !!

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Tommaso