MOSFET-enhancemement-depletion-n type-p type
n-channel: you must have \$V_{gs} &gt; V_{gs}(th)\$ to turn the FET "on".

n-channel enhancement mode: \$V_{gs}(th) &gt; 0\ V\$.

n-channel depletion mode: \$V_{gs}(th) &lt; 0\ V\$.

p-channel: you must have \$V_{gs} &lt; V_{gs}(th)\$ to turn the FET "on".

p-channel enhancement mode: \$V_{gs}(th) &lt; 0\ V\$.

p-channel depletion mode: \$V_{gs}(th) &gt; 0\ V\$.

In present times, depletion mode devices are rarely seen, so you probably want to focus your attention on how to use enhancement-mode devices.