There are many means for connecting speakers to amplifiers, some straightforward and others somewhat complex. Speaker cables are fairly heavy gauge unshielded cables.
Large cable is needed because of the high currents necessary to drive the speakers.
Small cable can not adequately carry the signal to drive large speakers, and will significantly degrade performance if it is used. Many types of connectors are used to hook speakers to amplifiers. Sometimes bare wire is used with 5-way binding posts on the speakers and amplifiers. This scheme works reasonably well for permanent installations, but is impractical for portable systems that must be taken apart frequently. Phone plugs, often used for line-level signals, are also frequently found on speakers.