user126793: Intuitively, I think minRelayFee is policy while minBlockTxFee is validation, but DEFAULT_MIN_RELAY_TX_FEE is in validation.h while DEFAULT_BLOCK_MIN_TX_FEE is in policy.h.

user101498: Both are policy. Both are about the same rule, just concern different parts of the code.
DEFAULT_MIN_RELAY_TX_FEE is about transaction relay (don't relay transactions that pay less than 1000 satoshis per kilo-vbyte), while DEFAULT_BLOCK_MIN_TX_FEE is about block creation (don't include transactions  paying less than 1000 satoshis per kilo-vbyte in block templates).

126793: <p>Intuitively, I think minRelayFee is policy while minBlockTxFee is validation, but <code>DEFAULT_MIN_RELAY_TX_FEE</code> is in <code>validation.h</code> while <code>DEFAULT_BLOCK_MIN_TX_FEE</code> is in <code>policy.h</code>.</p>
 101498: <p>Both are policy. Both are about the same rule, just concern different parts of the code.</p>
<p><code>DEFAULT_MIN_RELAY_TX_FEE</code> is about transaction relay (don't relay transactions that pay less than <code>1000</code> satoshis per kilo-vbyte), while <code>DEFAULT_BLOCK_MIN_TX_FEE</code> is about block creation (don't include transactions  paying less than <code>1000</code> satoshis per kilo-vbyte in block templates).</p>
