.trc and .trm files in Oracle 11g

What is .trc file?
Ans:Sql Trace Collection file

What is .trm file?
Ans:Trace map (.trm) file.Trace files(.trc) are sometimes accompanied by corresponding trace map (.trm) files, which contain structural information about trace files and are used for searching and navigation.

Doc ID 750982.1 explains this very well
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(Doc ID 750982.1):TRM Trace Files Getting Generated in 11g Database
From 11g onwards, all the trace files are found in ADR_HOME/trace directory.
There is usually one “.trm” file for each “.trc” file.
The files located in the TRACE directory, with the “.trm” extensions, are called Trace Metadata files. The metadata in .trm files describe the trace records stored inside of .trc trace files.
The Trace metadata allows tools, such as Adrci, to post process the trace information.

By deleting the .trm file, you make the .trc file unusable for post processing from ADR using ADRCI tool.
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<Related Topic>
What is ADR?
The Automatic Diagnostic Repository (ADR) is a file-based repository for storing diagnostic data. Because this repository is stored outside the database, the diagnostic data is available even when the database is down. As of Release 11g, the alert log, all trace and dump files, and other diagnostic data are also stored in the ADR.

What is an ADR HOME?
An ADR HOME is the root directory for all diagnostic dataa??traces, dumps, the alert log, and so ona??for a particular instance of a particular Oracle product or component.
The location of an ADR home is given by the following path, which starts at the ADR base directory:
diag/product_type/product_id/instance_id

Example of ADR HOMES:
diag/rdbms/orcl/ORCL1 (Product=rdbms, product_id=db_name=orcl, instance_id=ORACLE_SID=ORCL)
diag/asm/+asm/+ASM (Product=asm, product_id=+asm, instance_id=ORACLE_SID=+ASM)
diag/tnslsnr/node1/listener (Product=tnslsnr - SQL*NET Listener, product_id=hostname=node1, instance_id=listener name=listener)