# What are 2D reads in the Oxford MinIon?

Reading the Mash: fast genome and metagenome distance estimation paper, I see the reference to "2d reads" notion under the minION context (a sequencing technique)
e.g

    In both cases Mash was able to
correctly differentiate these closely related species
(ANI ≈ 95 %) using 43,806 and 91,379 sequences collected
from single MinION R7.3 runs of B. anthracis
Ames and B. cereus ATCC 10987, respectively (combined
1D and 2D reads) <----------  HERE.


But couldn't find any reference in Wikipedia or online papers to what it is
Can someone shed some light?