Standard & Non-Standard
Standard Script
Standard scripts in bitcoin are predefined and widely accepted transaction scripts.
They are well-tested and secure and nodes can quickly verify and relay them.
Below is a time line showing different output scripts types before and After Segwit:
bitcoin Transaction Relay Policy
Bitcoin Core will only relay transactions by default that pass the IsStandardTx() check. However, miners are still free to include (valid!) non-standard transactions in their blocks.
Non-Standard Script
Non-standard scripts in bitcoin are scripts that do not follow the commonly used templates for transactions.
Standard scripts, such as Pay-to-PubKey-Hash (P2PKH) and Pay-to-Script-Hash (P2SH), are widely recognized and accepted by nodes on the bitcoin network.
Any script that deviates from these templates is considered non-standard and it will not be relayed by the network.
They are valid but are not relayed by most nodes for safety reasons
Want Your Non-Standard Transaction Relayed and Mined?
To use a non-standard script, wrap your non-standard output scripts in p2sh/p2wsh output scripts. This makes your transaction appear standard and ensures it gets relayed and mined.