The x represents 10, meaning the mother tincture has been diluted to 1 part in 10. A 30x potency means the mother tincture has undergone the 1 in 10 dilution process 30 times.
The c represents 100, meaning that the mother tincture was diluted to 1 part in 100. A 30c potency means that the tincture has undergone this process of dilution 30 times.
Unlike conventional medications, the more diluted it is, the more potent the remedy. Lower potencies often are as effective as higher potencies once the correct remedy for the problem is identified.