According to the docs, ADA is an asset and a token, but they also indicate that tokens are on-chain versions of some off-chain asset. They also compare ADA and tokens in ways to imply that they are not the same kind of thing.
So, what is it? what is it called?
The terms cryptocurrency, token and asset are not mutually exclusive.
However, there are specific definitions that show a subtle difference between these three terms:
Cryptocurrency is a digital asset that circulates on the internet as a medium of exchange. It employs blockchain technology — a distributed ledger of transactions that is publicly available — and is secured by advanced cryptography. This revolutionary asset architecture allows for certainty that cryptocurrency coins and tokens cannot be double-spent even in the absence of a centralized intermediary. The first cryptocurrency to achieve mainstream success was Bitcoin which paved the way for the proliferation of many other cryptocurrencies.
Within the context of blockchain technology, a token generally refers to a unit of value for a programmable asset that is managed by a smart contract and an underlying distributed ledger. Tokens are the primary means of transferring and storing value on a blockchain network [...]. Tokens can also be designed to be either fungible or non-fungible, depending on a network's specific needs. And while many tokens are primarily used for simple transactions, an increasing number of blockchain projects are designing tokens encoded with a variety of wide-ranging use cases, primarily in regards to on-chain governance and network maintenance.
An asset is anything of monetary value that can be owned or purchased. Within the context of investing, assets can refer to a variety of financial and physical instruments, from stocks to real estate to gold to dollars. A bitcoin is a particular form of crypto or digital asset.
Ada is a digital token on the Cardano blockchain. Its currency symbol is the empty string - "".
It is similar to any other token that can be minted on the Cardano blockchain. However, there is a key difference.
A token are represented by a currency symbol which is the hash of the minting policy that is used to create it.
A minting policy describes how a token can be minted and burned, and no policy can mint or burn Ada, hence the empty string, which no policy can hash to.
