Decriminalization refers to laws aimed at rolling back harsh criminal penalties surrounding cannabis, typically by reducing minor possession and use from felonies or misdemeanors down to non-criminal citations or fines. Critically however, decriminalization does not actually legalize or regulate sales - buying and selling cannabis on a commercial unregulated scale remains strictly illegal and prohibited.
As the name implies, decriminalization seeks to ease draconian societal consequences on individuals for minor personal possession or consumption. But without establishing a legal market framework, it provides no systems for licensed growing or distribution - all buying and selling of cannabis remains criminal black market activity. Fines replace arrests and jail time for low level users under decriminalization, but fall well short of fully legalized regulated markets.
In contrast, broader full legalization statutes allow legislatures to not only remove all existing criminal and civil penalties for personal cannabis possession and use in legal amounts, but also establish regulated commercial market structures for legal sales, production, and taxation. Ultimately, legalization enables access and commerce for all law abiding adults while decriminalization simply spares them the very harshest criminal punishments.