Dynamic Frequency Selection plays a role in 5GHz frequencies that are shared with Terminal Doppler Weather Radar (TDWR). It is related to 802.11h.
DFS support is used during ACS/"survey" in hostapd to find and select free WLAN channels.
Many countries regulate operation of the 5GHz spectrum - see List_of_WLAN_channels & DFS/TPC channel information.
:!: Due to fast development, changing hardware, regulatory changes and compliance issues there can be interoperability issues.
:!: OpenWrt uses open source drivers with varying quality and upstream support. Sometimes they may be abandoned by the manufacturer, or no longer support some 5GHz operation due to regulatory changes.
:!: OEM proprietary drivers can sometimes offer DFS channel where OpenWrt opensource drivers cannot.
:!: There are different DFS schemes: DFS-FCC (USA), DFS-ETSI (Europe), DFS-JP (Japan).
:!: Try to use the non DFS channels if you have older wifi hardware/wifi clients.
In addition: See also FAQ - What does DFS mean? & Wireless FAQ section for more information.