ELI5 Zero - why was inventing it such a big deal?

What is zero's connection to algebra, Fibonacci and modern mathematics? What is the significance of it being both number and digit? Why was it so ground breaking when ancient civilizations discovered and started using the number 0? Finally... is infinity a number?   ... We explain like i'm five!     Thank you to the r/explainlikeimfive community, and specifically the following reddit users whose questions and responses formed the basis of this conversation: legalbarbecue19, habseligkeitderliebe, dennis_enzo, flobbley, e3rie_, nooneseemstomind & miguelmealie To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]