I believe that in db context, vectorization means batch processing column wise. Quoting the CockroachDB blog post:
Using vectorized processing in an execution engine makes more efficient use of modern CPUs by changing the data orientation (from rows to columns) to get more out of the CPU cache and deep instruction pipelines by operating on batches of data at a time.
Here is the link: https://www.cockroachlabs.com/blog/how-we-built-a-vectorized...