Ram

RAM is random access memory. It is different from storage memory. Storage memory is located at the back of your device--it comes in 8GB,16, 32,64. RAM is different.  It stores temporary memory. Let's say you open an app (from the storage memory). It opens in RAM. RAM is faster than the storage memory, so the device can read it faster. A shortage of RAM will slow your device down. If there is no RAM left, the app that is open will crash and take you back to the springboard. Shortage of ram will cause a laggy device.
To fix that problem you can download SBSettings, Free Memory Pro, or Free Memory. These apps/tweaks are NOT on the App Store so you must use Installous or Cydia.

SBSettings
1. Download SBSettings from Cydia
2. Slide your status bar and SBSettings comes down
3. Tap on "Processes"
4. Tap "Free Memory"
5. SBSettings frees some RAM. You can notice the difference at the bottom where it says "Availble Memory"
Requirements: iOS 2.0+



Free Memory Pro by Zakia Mahzabin
1. Download Free Memory Pro from Installous
2. Run the app. It is version 1.0 \
3. Tap the green refresh button and it will free ram.
     
 Requirements: iOS 3.0+                                                    



Free Memory
1. Download Free Memory from Installous (go to the page "Get Free Apps" for more info)
2. Run the app. If you downloaded version 2.0.1 then Free Memory will automatically free ram for you. You can notice the difference.
(the icon looks like this-- )
Once you free RAM, your device should run faster and smoother.
Requirements: iOS 4.0+