The three key characteristics of Big Data are commonly referred to as the 3Vs:

1. Volume - The massive scale of data
2. Velocity - The speed at which data is generated and processed
3. Variety - The different types and formats of data

Visibility is not one of the three key characteristics of Big Data. Some frameworks expand the concept to include additional Vs such as Veracity (data quality/trustworthiness) or Value (business value), but the core three are Volume, Velocity, and Variety.

Therefore, option C (Visibility) is the correct answer as it is not generally considered one of the three key characteristics of Big Data.