The original series is notorious for having a high volume of "filler" episodes (non-canon stories not found in the manga), particularly in Seasons 4 and 5.
Pro-tip: If you only want to watch the main story (canon) and skip the filler episodes, the watch time is significantly shorter. Roughly 40% of the original Naruto and Shippuden consists of filler material.
Ultimately, the franchise is split into two primary series: (Part 1) and Naruto: Shippuden (Part 2). Naruto (Part 1)
While the series aired as one continuous run in Japan, international releases (specifically the English dub) divided the series into .