Smart contracts can only query data that is stored on-chain. Oracles serve as the bridge between off-chain ‘real-world information' and the blockchain. They collate and verify through consensus real-world information and then submit it on-chain for use by smart contracts.
For example, an Oracle may collect and verify commodity-price information that is then recorded on-chain so it can be used as reliable price data by a trading-related smart contract.
In the case of Analog, our Oracles verify real-world time data prior to logging it to the Timegraph.