Nodding through is when an MP is counted as having voted because, although they are present on the parliamentary estate, they are unable to pass through the division lobby because they are physically unwell or they have a small child with them.
Decisions made 'on the nod' are decisions made with no debate or division (vote). The Chair simply reads out the question to be decided and takes an oral vote. If there are no objections, the question is recorded as having been agreed to.
A decision taken on the nod is generally on a non-contentious question or one whose points of contention have been - or will be - addressed at another time.