It depends on:
* Genre: Epic poems (like The Odyssey) can be thousands of lines long. Long narratives or verse novels are also considered extended.
* Form: Some forms, like sonnets, are inherently short. Others, like blank verse, can be quite long.
* Individual poet's intention: What one poet considers "extended" might be just a regular-length poem for another.
General guidelines:
* Short poems: Under 100 lines
* Medium-length poems: 100-500 lines
* Long poems: Over 500 lines (and often stretching into the thousands)
Key takeaway: "Extended" signifies a poem longer than the average. It's more about the poem's scope and impact than a precise line count.