What do white numbers with blue background mean?

Solution 1:

This is affinity. It's not a damage type but rather a fancy word for experience.

If you see this number it means you just gained experience for an action (In the case of your picture: Killing an enemy)

Note that this number indicates the total affinity you gained through this action. Affinity is distributed into your weapons based on your loadout and the action you perform.

The affinity "split" can be found here.

• Kill an enemy with a Warframe ability. All of the Affinity goes to the Warframe.
• Kill an enemy with a weapon. Half of the Affinity goes to the Warframe and half to the killing weapon.
  • Be near an allied Tenno when they kill an enemy. When within 50 meters of an ally when they kill an enemy, you gain the same total Affinity, distributed as specified above. This doesn't reduce the Affinity gained by the killing player, and doesn't reduce the Affinity gained by other nearby allies. This applies to Archwing mode with much larger ranges for shared affinity.
• Use a Warframe/Archwing ability. Affinity equal to the base energy cost, in most cases.
  • As of Hotfix 19.5.4, it is still bugged. User gains no affinity from Warframe ability use.
• No weapons equipped. All of the Affinity goes to the Warframe.
• This applies when the only equipped weapons are overridden by ability-created ones. (E.g. Using Exalted Blade while only having a melee weapon equipped.)
• Hack a terminal. 50 Affinity.
• Complete an objective.
• Complete a Challenge. 1,000 or 5,000 Affinity, depending on the particular challenge.
• Collect an Affinity Orb. 100 Affinity.
• Scanning with the Codex Scanner.
  • Scanning objects. 10 Affinity.
  • Scanning enemies. Affinity equal to 1/3 of gain upon killing the enemy (rounded down).
  • Stealth scan. Affinity equal to gain upon killing the enemy.

Companion Affinity

Companions gain their own Affinity, similar to Tenno.

• The Companion kills an enemy. Total Affinity upon kills is equal to that gained by Tenno. The owner of the Companion gains no Affinity.
  • Kills with its weapon. 50% Affinity is split between the Companion and its weapon.
  • Kills with an ability. 100% Affinity to the Companion.
• The Companion uses an ability. Amount varies by ability. 100% goes to the Companion.
• A nearby Tenno, but not the Companion's owner, kills an enemy. Affinity gained by the Companion does not detract from that gained by its owner.
  • 50% Affinity is split between the Companion and its weapon.
  • 100% Affinity to the Companion in the absence of a weapon.