For the most part, sparqee is right about what an audio interface is. If you look at some interfaces even the companies that makes them call them sound cards. The Terratec EWS88MT is a sound card it can be run in tandem to record up to 32 anologe tracks simultaniously. It also has near zero latency. It has 8 anologe ins and 8 outs. Another good card is...
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I have a MOTU 24i interface that uses a 324 or 424 Card. Cards can be called interfaces in most cases but you usually won't ever call an interface a card. If that makes any sense. A card usually goes into a PCI or PCIe or PCIX or even an ISA slot. Usually a true interface doesn't go into any slot. If you want to find a multi track sound card, you would look under audio interfaces.