The data highways inside the computer through which the information moves from one spot to another. Address bus wires carry the address of where the data is coming from or where it is going to. This tells the various components in the computer whether they should receive data from or supply data onto the data bus wires. They also carry timing information to help synchronize the various parts of the computer so they are all doing the right thing at the right time. The instructions that tell the CPU what to do.
Programs are fundamentally the same as data.
A program is really just a bunch of special codes that tell the computer what operation to perform. The OS is always running and never goes away. User programs tell the computer what to do with things the OS has taught it to do. These are the programs that really do the useful work. Microsoft Word, Excel, Lotus 123, WordPerfect, etc. are examples of user programs.