Lava/BS

Java Edition:

Name	Default value	Allowed values	[hide]Description
level	0	0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15	If bit 0x8 is set, this fluid is "falling" and spreads only downward. At this level, the lower bits are essentially ignored, since this block is then at its highest fluid level. This level is equal to the falling lava above, equal to 8 plus the level of the non-falling lava above it. The lower three bits are the fluid block's level. 0 is the highest fluid level (not necessarily filling the block - this depends on the neighboring fluid blocks above each upper corner of the block). Data values increase as the fluid level of the block drops: 1 is the next highest, 2 lower, on through 7, the lowest fluid level. Along a line on a flat plane, lava drops one level per meter in the Nether and two everywhere else. So in the End and Overworld, only 2, 4 and 6 are used.

Bedrock Edition:
Lava and flowing lava

Name	Metadata Bits	Default value	Allowed values	Values for Metadata Bits	[hide]Description
liquid_depth	0x1 0x2 0x4 0x8	0	0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15	0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15	If bit 0x8 is set, this fluid is "falling" and spreads only downward. At this level, the lower bits are essentially ignored, since this block is then at its highest fluid level. This level is equal to the falling lava above, equal to 8 plus the level of the non-falling lava above it. The lower three bits are the fluid block's level. 0 is the highest fluid level (not necessarily filling the block - this depends on the neighboring fluid blocks above each upper corner of the block). Data values increase as the fluid level of the block drops: 1 is the next highest, 2 lower, on through 7, the lowest fluid level. Along a line on a flat plane, lava drops one level per meter in the Nether and two everywhere else. So in the End and Overworld, only 2, 4 and 6 are used.