When considering the data size threshold that one needs to be working with in order for what they are doing to be considered Big Data analytics, it should be noted that:

The data size threshold can change; it changes when new metric prefixes for sizes are added.

The data size threshold cannot change; it is measured in Petabytes.

The data size threshold cannot change; it is measured in Terabytes.

The data size threshold can change; it changes relative to time because our data capabilities advance with time.