What is the meaning of [security] on the Debian packages web

What is the meaning of [security] in the title like in these packages:

  • https://packages.debian.org/buster/nginx-extras
  • https://packages.debian.org/stretch/openssl ?

It refers to the fact that the package received a security update.

Edit: I'm not able to cite a reference, it's just my take from reading the source code. Specifically, the code checks if the latest version is available from main, or a different section. If it's different, the suite name is included and the suite is marked accordingly with red color. This is also why this not only applies to packages with a security update, but also to packages from contrib or non-free.

For reference, the source code:

if ($p{versions}) {
    warn "\tversions=$p{versions}\n" if DEBUG;

    $html .= "\n<dt><a href='$p{name}'$id>$p{name}</a> ($p{versions})";
    $id = "";
    $html .= " [<strong class='pmarker'>$p{section}</strong>]"
    if $p{section} ne 'main';
    $html .= " [<strong class='pmarker'>$p{archive}</strong>]"
    if $p{archive} ne 'us';
    $html .= "</dt>\n<dd";

    $txt .= "\n$p{name} ($p{versions})";
    $txt .= " [$p{section}]" if $p{section} ne 'main';
    $txt .= " [$p{archive}]" if $p{archive} ne 'us';
    $txt .= " ";

    if ($p{trans_desc}) {
    foreach my $lang (@LANGUAGES) {
        my ($sdesc, $sdesc_html, $desclang) = ($p{desc},
                           encode_entities($p{desc}, '<>&"\''),
                           'en');
        if ($p{trans_desc}{$lang}) {
        $sdesc = $p{trans_desc}{$lang};
        $sdesc_html = encode_entities($sdesc, '<>&"\'');
        $desclang = $lang;
        }

        $html .= $s{begin}{$lang};
        $html .= " lang='$desclang'" if $desclang ne $lang;
        $html .= ">$sdesc_html$s{end}{$lang}";
    }
    } else {
    $html .= " lang='en'>".encode_entities($p{desc}, '<>&"\'');
    }
    $html .= "</dd>";
    $txt .= $p{desc};
}

It means that this version of the package is a security update.

from: https://lists.debian.org/debian-www/2004/03/msg00158.html