wrote

I worked for a rock band years ago, doing sound and lighting. Our
"gaffer tape" was just plain duct tape. I never knew there was a
difference. The duct tape held the cords to the floor and stuff like
that, yet it came off fairly easily when the concert was over. You
now got me asking what actual "gaffer tape" is? What does it look
like, what color is it, etc.?

I recently saw gorilla tape in the store. Never tried it. I thought
that too was just another name for duct tape. They also sell gorilla
glue.....

Since some people are dickheads and won't share their hard-won information
from Google, I offer the following from Wikipedia: (and for free, too)

Google does occasionally prove handy.

From Wikipedia, the free encyclopedia
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Gaffer tape, sometimes shortened to gaff tape (especially by theater and
photographic professionals), or made possessive, as "gaffer's tape", is a
strong, pressure-sensitive, cotton cloth adhesive tape. It is an essential,
all-purpose tool on theater, film and television productions as well as live
performances and any other kind of stage work.[1]

The most common use for gaffer tape is securing cables to the stage floor or
other surface, either for safety or to keep them out of view of the audience
or camera. Camera assistants use short strips of different colors to lay
blocking markers for actors. Similarly, a narrow version of gaffer tape,
called spike tape, is used in theatre productions for floor layout. It is
also used whenever a quick ad-hoc fix is required, from temporarily
attaching fixtures or props, to salvaging a broken piece of production
equipment. In the absence of console tape or artist tape, live sound
engineers may use a strip of white gaffer tape along the bottom of a mixing
board, to label the channels used for a particular show.

The tape is manufactured in many colors, including fluorescent and custom
colors, but the most common variety is matte black or dull grey. A matte
finish keeps the tape from reflecting light so the tape blends in with the
typical stage floor of a theatre.[2] It is easily torn by hand so no cutting
tools are necessary. The adhesive used is a high quality synthetic rubber
which leaves little or no residue when removed.[3] It usually comes in
2"-wide rolls, and the cloth composition allows a consistent tear, which
means it easily tears into two 1" strips, if needed. Gaffer tape should not
be compared to duct tape, a far cheaper product which does not tear cleanly
and leaves a residue when removed. [4]

It is likely named for the gaffer, the head of the lighting department on a
film crew. When cables are taped down on a stage or other surface, either
for safety or to keep them out of view of the audience or camera,[5] they
are said to be gaffed or gaffered.