SOAP is an acronym for Simple Object Access Protocol and basically what it is used for is exchanging XML based messages.
It is neither a package or an interface that Apache Axis uses. Although it could be what they named a package within their code but that isn't the point. SOAP is merely a protocol for exachanging messages and Axis is a tool that was designed to aid in producing and exchanging those messages that follow the SOAP standard.
Think about it this way. There is no package call TCP/IP. It is just the protocol that many network devices follow so they can talk to each other.