There are several different types of SD cards, including:

1. SDSC (SD Standard Capacity) - These cards have a storage capacity of up to 2GB.

2. SDHC (SD High Capacity) - These cards have a storage capacity of up to 32GB.

3. SDXC (SD Extended Capacity) - These cards have a storage capacity of up to 2TB.

4. SDUC (SD Ultra Capacity) - These cards have a storage capacity of up to 128TB.

In addition to different types, there are also different grades of SD cards, which are defined by their speed class rating. This rating indicates the minimum sustained write speed of the card, which is important for applications such as recording video or capturing high-resolution photos. The current speed classes are:

1. Class 2 - Minimum sustained write speed of 2MB/s.

2. Class 4 - Minimum sustained write speed of 4MB/s.

3. Class 6 - Minimum sustained write speed of 6MB/s.

4. Class 10 - Minimum sustained write speed of 10MB/s.

5. UHS Speed Class 1 (U1) - Minimum sustained write speed of 10MB/s.

6. UHS Speed Class 3 (U3) - Minimum sustained write speed of 30MB/s.

7. Video Speed Class (V6, V10, V30, V60, V90) - Minimum sustained write speeds designed for video recording at various resolutions and bitrates.

It's important to note that not all devices support all types or grades of SD cards, so it's important to check your device's specifications before purchasing an SD card.