1. Open Disk Utility (System>Administration) or type “df” in a terminal
2. Check Out the left panel, you'll see every disk connected to your computer along with each partition nested beneath
3. Click on desired partition (looking at the size helps)
4. In the right panel, the fifth line down will say something like /dev/sda2; the sda2 what you're looking for

This will work for USB drives, hard drives, SD cards, etc. Note that some of the guides' steps require just the disk reference (e.g. sda), some the full name (e.g. sda2), while others require only the number (e.g. 2).

1. Open Disk Utility (Applications>Utilities)
2. Select your USB drive and hit Cmd+I
3. Look for Disk Identifier (e.g., disk1s2)

This will work for USB drives, hard drives, SD cards, etc. Note that some of the guides' steps require just the disk reference (e.g. disk1), some the full name (e.g. disk1s2), while others require only the number (e.g. 2).