What does "bumped transaction" mean?

Database header page information:
Flags 0
Checksum 12345
Generation 3218036
Page size 8192
ODS version 10.1
Oldest transaction 3218004
Oldest active 3218005
Oldest snapshot 3218005
Next transaction 3218006
Bumped transaction 1
Sequence number 0
Next attachment ID 0
Implementation ID 19
Shadow count 0
Page buffers 8192
Next header page 0
Database dialect 3
Creation date Apr 19, 2007 13:58:18
Attributes force write, no reserve

Variable header data:
Sweep interval: 20000
*END*

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