https://youtu.be/kzYwZpBBx_Q?list=PLaAxhhFb7OVElRJ8Su_C2Xu2uA7WiBKKz&t=59

Well... technically not entirely correct.

A Koblitz curve in the original sense proposed by Neal Koblitz is defined over a binary extension field.

secp256k1 is sometimes informally referred to as a "Koblitz curve" because SECG redefined the term in their 

Parameters associated with a Koblitz curve admit especially efficient implementation. The name Koblitz curve is best-known when used to describe binary anomalous curves over F_{2m} which have a, b ∈ {0, 1} [Kob92]. Here it is generalized to refer also to curves over F_p which possess an efficiently computable endomorphism [GLV01].

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https://youtu.be/kzYwZpBBx_Q?list=PLaAxhhFb7OVElRJ8Su_C2Xu2uA7WiBKKz&t=59
Well... technically not entirely correct.
A Koblitz curve in the original sense proposed by Neal Koblitz is defined over a binary extension field.

secp256k1 is sometimes informally referred to as a "Koblitz curve" because SECG redefined the term in their [sec2 paper](https://www.secg.org/sec2-v2.pdf):

> Parameters associated with a Koblitz curve admit especially efficient implementation. The name Koblitz curve is best-known when used to describe binary anomalous curves over F_{2m} which have a, b ∈ {0, 1} [Kob92]. Here it is generalized to refer also to curves over F_p which possess an efficiently computable endomorphism [GLV01].