Data-oriented design
A way of structuring code around how the data actually sits in memory and is read, rather than around objects and hierarchies — on the blunt premise that memory access, not instructions, is the bottleneck.
On modern hardware a cache miss costs hundreds of cycles while the computation is nearly free. So you group data into parallel arrays (struct of arrays) so a loop reads just the fields it needs, tightly packed into cache lines, instead of hopping around via pointers between fat objects.
Mike Acton (Insomniac Games) nailed the stance down in his 2014 GDC talk. The mindset is the very engine behind entity component systems, and stands in declared opposition to naive object orientation.