O que é Effective tick size?

The effective tick size is the smallest difference between the fee-adjusted prices at which one side can trade when the same instrument is quoted on venues with different fees: with take fees $f_1$ and $f_2$ and a tick $\delta_{\mathrm{tick}}$, the fee-adjusted asks $p+f_1$ and $p+f_2$ interleave with gaps $|f_1-f_2|$ and $\delta_{\mathrm{tick}}-|f_1-f_2|$ (fees reduced modulo the tick).