What is an irregular period exactly?

[Folicacid]

Conflicting info on the web!

Is it a cycle length that is outside of the norm of 25 to 34 days OR is it periods that are different lengths on a month to month basis?

for example: My last four periods were:
27 days, 34 days, 27 days, 25 days.

Is that therefore irregular? I felt as though the 34 days was due to travel and being quite stressed with work.

A "normal" cycle is a cycle length of between 21 and 35 days or with less than 4 days of variation from month to month.

Thanks Attila.